[1] The railroad, whose owners were Union sympathizers, proved crucial to the North's success during the American Civil War, which caused considerable damage to the system.

At the end of 1970, the B&O operated of 4,535 miles of mainline track, not including the Staten Island Rapid Transit (SIRT) or the Reading Railroad and its subsidiaries.

By crossing the Appalachian Mountains, a technical challenge, it would link the new and booming territories of what at the time was the West, particularly Ohio, Indiana, and Kentucky, with the east coast rail and boat network, from Maryland northward.

However, the 1831 DeWitt Clinton locomotive, running between Albany and Schenectady, New York, demonstrated speeds of 25 miles (40 km) per hour, dramatically decreasing the cost of transportation and announcing the coming end of the canal and turnpike (road) systems, many of which were never completed since they were or would soon be obsolete.

In New York, political support for the Erie Canal detracted from the prospect of building a railroad to replace it, whose full length did not open until 1844.

On February 27, 1827, twenty-five merchants and bankers studied the best means of restoring "that portion of the Western trade which has recently been diverted from it by the introduction of steam navigation.

The railroad fed tens of millions of dollars of shipments to and from Baltimore and its growing hinterland to the west, thus making the city the commercial and financial capital of the region south of Philadelphia.

The railroad, formally incorporated April 24, was intended to provide a faster route for Midwestern goods to reach the East Coast than to the hugely successful but slow Erie Canal across upstate New York.

[11] Construction began on July 4, 1828, when Charles Carroll of Carrollton (the last living signer of the Declaration of Independence) performed the groundbreaking by laying the cornerstone.

The narrow strip of available land along the Potomac River from Point of Rocks to Harpers Ferry caused years of legal battles between the B&O and the Chesapeake and Ohio (C&O) Canal, as both sought to exclude the other from its use.

[17]: 157  This line joined to the original mainline at Relay, Maryland, crossing the Patapsco River on the Thomas Viaduct (which remains one of the B&O's signature structures).

The railroad decided to construct two inclined planes, one on each side of the ridge, along which teams of horses, and perhaps steam-powered winches, would assist pulling the trains uphill.

On May 24, 1844, the line was officially opened as Samuel F. B. Morse sent his famous words, "What hath God wrought", from the B&O's Mount Clare station to the Capitol by telegraph.

[28][31][32] Garrett reported with evident relief the next day that aside from the cut telegraph line, which was quickly repaired, there had been no damage to any B&O track, equipment, or facilities.

The B&O became crucial to the Federal government during the Civil War, being the main rail connection between Washington, D.C., and the northern states, especially west of the Appalachian mountains.

Charles Town's mayor also wrote, threatening to cut the B&O's main line by destroying the long bridge over the Potomac River at Harpers Ferry, and Garrett also received anonymous threats.

The Secretary of War agreed to station troops to protect the North Central, the Pennsylvania Railroad, and even the PW&B, but flatly refused to help the B&O, his main competition.

Stonewall Jackson initially permitted B&O trains to operate during limited hours over the approximately 100 miles from Point of Rocks to Cumberland.

Since Jackson cut the B&O main line into Washington for more than six months, the North Central and Pennsylvania Railroads profited from overflow traffic, even as many B&O trains stood idle in Baltimore.

Garrett tried to use his government contacts to secure the needed protection, from Maryland Delegate Reverdy Johnson to General George McClellan and Treasury Secretary Salmon P. Chase.

As preparations for the battle progressed, the B&O provided transport for federal troops and munitions, and on two occasions Garrett was contacted directly by President Abraham Lincoln for further information.

This provided a direct rail connection to Columbus, Ohio, and the lease marked the beginning of a series of expansions to the west and north.

After a second reduction in wages was announced in the same year, workers began the Great Railroad Strike of 1877 on July 14 in Martinsburg, West Virginia.

West Virginia Governor Henry M. Mathews sent in state militia units to restore train service but the soldiers refused to fire on the strikers.

The 10th president, Charles F. Mayer, spearheaded the development of the Baltimore Belt Line, which opened in 1895, and recruited engineer Samuel Rea to design it.

The ferry operation continued until 1901 when the trackage rights agreement concluded as part of the construction of Washington Union Station saw the south end of the branch realigned to link to the PRR trackage in Anacostia, across the Anacostia Railroad Bridge, into the Virginia Avenue Tunnel, through Southwest Washington, D.C., to Potomac Yard in Alexandria, Virginia.

SCL Industries was renamed the Seaboard System Railroad (SBD) in 1983, the same year that the Western Maryland Railway was completely absorbed into the B&O.

On April 30, 1987, the B&O's corporate existence ended when it was absorbed into the Chesapeake and Ohio Railway, which merged into CSX Transportation on August 31 of that year.

When CSX established the B&O Railroad Museum as a separate entity from the corporation, it donated some of the former B&O Mount Clare Shops in Baltimore, including the Mt.

In May 2023, GE ES44AH unit #1827 entered service, being repaired and painted at CSX shops in Waycross, GA under the honorary B&O scheme similar to that of the three F40PH locomotives.